Facebook knows how your hometown feels about gay marriage

In March of this year, a wave of equals signs swept Facebook. More than three million users around the world were changing their profile pictures to variations of logos from various LGBT rights organizations. The effort was meant to show support for the legalization of gay marriage, an issue then being heard before the United States Supreme Court.

On Monday, a team of Facebook data scientists posted an analysis of the phenomenon and found it to be far-reaching, albeit geographically clustered in areas where widespread support for LBGT rights was already prevalent.

The analysis found that, of the more than 3 million people who changed their profile picture in support of marriage equality, 2.77 million lived in the United States. Other English-speaking countries like Canada, Australia, and the United Kingdom also saw tens of thousands of people participate, although the vast majority were in the U.S..

Of U.S. Facebook users who had at least one friend display an equals sign, 1.9 percent then changed their photo to one supporting the campaign. This "susceptibility" rate in other countries with significant numbers of participants was substantially lower—Canada and Australia both saw 0.7 percent, while Germany and Ireland boasted 0.5 percent.

The trend’s distribution throughout the United States was uneven and ran along fairly predictable lines. Adoption was much more prevalent in the comparatively progressive West Coast, Northeast, and Great Lakes regions, while it experienced much less penetration into the conservative areas of the Deep South and Midwest.

There were some exceptions, however—primarily left-leaning college towns nestled inside of largely conservative regions. The presence of universities Austin, Texas and Missoula, Montana makes them islands of red amid a sea of yellow.

The researchers even found surprisingly deep divisions within individual metro areas.

In New York City, there was far more adoption in Manhattan, Brooklyn, and Queens than in the outer boroughs:

Similar clustering was present in Chicago and Los Angeles:

In the San Francisco Bay Area, on the other hand, the prevalence was far more uniform. In fact, the counties of San Francisco and San Mateo, the latter being the location of Silicon Valley tech giants like Facebook itself, had among the highest participation rates of anywhere in the world.

‟These striking differences at the level of urban areas could be the either the result of large geographical differences in terms of support for marriage equality, or they could be the result of lack of connectivity between social networks that made the phenomenon less likely to catch on in certain regions,” wrote the researchers.

‟As with most social phenomena, we are probably dealing with a combination of both factors, but we will leave the exact diffusion mechanism to further work.”